Within the context of a tertiary referral center for perinatal care, this investigation proposes to characterize human placental Glutathione S-transferase and Aryl hydrocarbon hydroxylase with respect to (1) their activities throughout the second half of gestation, (2) their responsiveness to specific maternal xenobiotic exposures (maternal cigarette smoking or anticonvulsant therapy), and (3) their molecular components. These data will also be correlated wit fetal outcome. Previously described methodologies for the resolution of hepatic microsomal cytochrome P-450 monooxygenase systems and cytosolic Glutathione S-transferase will be modified for investigation of placental Aryl hydrocarbon hydroxylase and enzymatic glutathione conjugation. These studies are intended to provide a phenomenologic and biochemical foundation from which future investigations of human environmental responsiveness, perinatal xenobiotic metabolism and teratogenesis may proceed.